The present invention relates generally to a system for diagnosing and controlling a high-pressure fuel system for an in-cylinder fuel injection engine. More specifically, the invention relates to a system for diagnosing the abnormality of a high-pressure fuel system of an in-cylinder fuel injection engine, and a control system capable of coping with the abnormality of the high-pressure fuel system of the in-cylinder fuel injection engine.
Conventionally, there has been known an in-cylinder fuel injection engine for injecting a fuel directly into a cylinder (a combustion chamber) to ignite and burn the injected fuel by means of a spark plug, in order to improve fuel consumption, engine output and exhaust emission.
As disclosed in Japanese Patent Laid-Open No. 2-169834 or 8-177699, an in-cylinder fuel injection engine of this type must maintain a fuel pressure fed to an injector to be a high pressure in order to inject the fuel directly into a cylinder against the cylinder pressure, so that the fuel is fed from a fuel tank to a high pressure pump by means of a low pressure pump (a feed pump) to raise the pressure of the fuel by means of the high pressure pump to feed a high pressure fuel to the injector.
That is, the high pressure pump does not have a sufficient fuel self-priming power, so that a low pressure pump, such as an electric feed pump, is provided upstream of the high pressure pump to feed the fuel from the fuel tank to the high pressure pump by means of the low pressure pump.
In addition, in order to stably feed the fuel to the high pressure pump, the low pressure pump has a discharge capacity which is the same as or more than the maximum discharge capacity of the high pressure pump, and a low pressure regulator is provided for regulating the fuel pressure fed from the low pressure pump to a predetermined fuel pressure to feed the pressure regulated fuel to the high pressure pump.
Moreover, in an in-cylinder fuel injection engine of this type, a fuel injection pulse width defining the fuel injection quantity is set on the basis of the engine operating condition, and a drive signal indicative of the fuel injection pulse width is outputted to an injector to obtain a desired fuel injection quantity by the injection-valve opening period of the injector based on the fuel injection pulse width. Therefore, the fuel pressure of the high-pressure fuel system for feeding the fuel from the high pressure pump to the injector must be held at a predetermined fuel pressure. For that reason, the pressure of the fuel raised by the high pressure pump is regulated to a predetermined controlled fuel pressure by means of a high pressure regulator, and a high pressure fuel of the controlled fuel pressure is fed to the injector.
However, if something is wrong with the high pressure pump or high pressure regulator, which form the high-pressure fuel system, or if the fuel leaks out of the high-pressure fuel system, the fuel pressure of the high pressure fuel fed to the injector can not be maintained to the predetermined controlled fuel pressure, so that the controllability of fuel injection deteriorates. In addition, if the injector has abnormality, such as defective injection-valve opening, a desired fuel injection quantity can not be obtained, so that the controllability of fuel injection deteriorates.
Then, if the degree of the abnormality of the high-pressure fuel system increases, the controllability of fuel injection more deteriorates, so that the engine combustion state deteriorates. If the degree of the abnormality remarkably increases, the engine may be inoperable or damaged.